Apparatus for motor synchronization

ABSTRACT

A DC electric motor includes an internal programmable element that permits it to be synchronized to an external reference signal. To that end, the motor includes a rotor capable of rotating at a rotational speed, rotor circuitry that controls the rotational speed of the rotor, and an input to receive the noted external reference signal, which indicates a preset speed. In addition, the motor also includes the noted programmable element, which is operatively coupled with the input and the rotor circuitry within the motor. The programmable element is capable of comparing the external reference signal with the rotational speed of the rotor and, consequently, controls the rotor circuitry based upon the comparison of the external reference signal and the rotational speed of the rotor.

[0001] This application claims priority from U.S. patent applicationSer. No. 09/731,884, filed Dec. 7, 2000, entitled “Motor SynchronizationApparatus,” and U.S. provisional patent application Ser. No. 60/169,568,filed Dec. 8, 1999, entitled “Motor Synchronization Apparatus,” thedisclosures of which are incorporated herein, in their entireties, byreference.

FIELD OF THE INVENTION

[0002] This invention generally relates to motors and, moreparticularly, the invention relates to synchronizing DC electric motoroperation to a reference frequency.

BACKGROUND OF THE INVENTION

[0003] Many systems utilize multiple D.C. motors in parallel for variousreasons. For example, multiple fans are utilized to cool elevators, andmany computer systems utilize two or more fans to cool internalelectronic components. Such systems often are preconfigured so that thefans are synchronized to operate at a substantially identical rotationalspeed. In practice, however, although ideally set to operatesynchronously, such fans often operate at different speeds. When fansare not synchronized, they often generate a noise that many people tendto consider annoying.

SUMMARY OF THE INVENTION

[0004] In accordance with one aspect of the invention, a DC electricmotor includes an internal programmable element that permits it to besynchronized to an external reference signal. To that end, the motorincludes a rotor capable of rotating at a rotational speed, rotorcircuitry that controls the rotational speed of the rotor, and an inputto receive the noted external reference signal, which indicates a presetspeed. In addition, the motor also includes the noted programmableelement, which is operatively coupled with the input and the rotorcircuitry within the motor. The programmable element is capable ofcomparing the external reference signal with the rotational speed of therotor and, consequently, controls the rotor circuitry based upon thecomparison of the external reference signal and the rotational speed ofthe rotor.

[0005] The programmable element preferably is a processor. Inillustrative embodiments, the programmable element is capable ofcontrolling the rotor circuitry to increase the rotational speed of therotor if it is determined that the rotational speed of the rotor is lessthan the preset speed indicated in the external reference signal. In asimilar manner, the programmable element also may be capable ofcontrolling the rotor circuitry to decrease the rotational speed of therotor if it is determined that the rotational speed of the rotor isgreater than the preset speed indicated in the external referencesignal.

[0006] Among other things, the rotor circuitry may include at least oneof switching circuitry and commutation circuitry. The motor also mayinclude a housing containing the rotor circuitry and programmableelement. In some embodiments, the programmable element is programmed todetect an error condition with the external reference signal. Theprogrammable element consequently sets the rotational speed of the rotorto a selected speed if the error condition is detected. By way ofexample, the error condition may be considered to have occurred if thepreset speed is not within a prescribed range of speeds. The motor alsomay include an internal clock that produces an internal clock signal.The selected speed thus may be based upon the internal clock signal. Themotor may be used as a fan and thus, include an impeller coupled withthe rotor.

[0007] In accordance with another aspect of the invention, a motorapparatus has a first DC electric motor capable of rotating at a firstrotational speed and having a first internal processor, and a second DCelectric motor capable of rotating at a second rotational speed andhaving a second internal processor. In addition, the motor apparatusalso includes a master clock that produces a reference signal indicatinga preset speed. The master clock is coupled with both the first DCelectric motor and the second DC electric motor. In illustrativeembodiments, the first processor is capable of controlling the firstrotational speed to be synchronized with the reference signal, and thesecond processor is capable of controlling the second rotational speedto be synchronized with the reference signal.

[0008] In some embodiments, the first DC electric motor includes a firstimpeller, and the second DC electric motor includes a second impeller.The first processor may include a first reference input, and the secondprocessor includes a second reference input. The first and secondreference inputs thus may be coupled with the master clock to receivethe reference signal. In other embodiments, the first rotational speedand second rotational speed are substantially identical. Moreover, themotor apparatus may include a first motor housing containing the firstDC electric motor, and a second motor housing containing the second DCelectric motor.

[0009] The first DC electric motor may include commutation circuitrythat is controlled by the first processor. The first internal processormay be programmed to detect an error condition with the reference signaland, consequently, set the first rotational speed to a selected speed ifthe error condition is detected. The error condition may be consideredto have occurred if the preset speed is not within a prescribed range ofspeeds. The first internal processor may include an internal clock thatproduces an internal clock signal. Accordingly, the selected speed maybe based upon the internal clock signal.

[0010] In accordance with another aspect of the invention, a DC electricmotor includes a rotor capable of rotating at a rotational speed, rotorcircuitry that controls the rotational speed of the rotor, and areceiving means for receiving an external reference signal indicating apreset speed. In addition, the motor also may include a comparing meansfor comparing the external reference signal with the rotational speed ofthe rotor. The comparing means includes means for controlling the rotorcircuitry based upon the comparison of the external reference signal andthe rotational speed of the rotor. The comparing means preferably isinternal to the motor.

[0011] In accordance with still another aspect of the invention, a rotorcircuit for controlling the speed of a rotor (i.e., the rotor being apart of a DC electric motor) includes switching circuitry that, at leastin part, controls the rotational speed of the rotor, and an input forreceiving an external reference signal indicating a preset speed. Inaddition, the rotor circuit also include a programmable elementoperatively coupled with the input and the switching circuitry. Theprogrammable element compares the speed of the rotor with the presetspeed indicated in the reference signal. The programmable elementcontrols the switching circuitry based on the comparison of the presetspeed and the speed of the rotor. The switching circuitry andprogrammable element are internal to the motor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The foregoing and advantages of the invention will be appreciatedmore fully from the following further description thereof with referenceto the accompanying drawings wherein:

[0013]FIG. 1 schematically shows a motor apparatus having multiplemotors synchronized in accordance with preferred embodiments of theinvention.

[0014]FIG. 2 schematically shows an exemplary DC brushless fan that maybe configured with the synchronization circuit in accordance withpreferred embodiments of the invention.

[0015]FIG. 3 schematically shows an impeller of the fan shown in FIG. 2.

[0016]FIG. 4 schematically shows coil energization and synchronizationcircuits configured in accordance with one embodiment of the invention.

[0017]FIG. 5 shows a preferred process of synchronizing the rotationalspeed of the motor with a reference frequency.

[0018]FIG. 6 schematically shows coil energization and synchronizationcircuits configured in accordance with another embodiment of theinvention.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0019] In illustrative embodiments of the invention, each one of aplurality of cooperating DC electric motors includes an internalprocessor that synchronizes motor operating speed with an externallyreceived reference signal. Details of various embodiments are discussedbelow.

[0020]FIG. 1 schematically shows a motor apparatus 2 having multiplemotors synchronized in accordance with preferred embodiments of theinvention. More particularly, the motor apparatus 2 includes N DCelectric motors (i.e., identified as motor 1, motor 2, motor 3 . . .motor N, and generally identified as motors 4) that each aresynchronized to rotate at a rotational speed as specified by a referencesignal received from a master clock 6. Accordingly, each motor 4 has aninternal motor synchronization circuit (discussed in detail below withreference to FIGS. 4 and 6) that receives the reference signal from themaster clock 6, and rotates its respective rotor at a rotational speedthat is related to the reference frequency of the reference signal. Thereference signal may be any signal used to control the circuitrydiscussed below. To that end, the reference signal may be, among othertypes of waves, a square wave, a saw-tooth wave, or an AC signal.

[0021] The motor apparatus 2 may be any device known in the art thatutilizes multiple motors 4. For example, the motor apparatus 2 mayinclude parallel and/or serial motors. In illustrative embodiments, themotors 4 are implemented as plural fans for cooling a computer system.Accordingly, various embodiments are discussed with reference to a fan.It should be noted, however, that discussion of a fan is by example onlyand not intended to limit the scope of the invention.

[0022]FIG. 2 schematically shows an exemplary DC brushless fan that maybe configured with the synchronization circuit discussed herein. Asknown in the art, the fan includes a housing 11 with a front surface 12,a rear surface 13, and venturi 14 extending between the front and rearsurfaces 12 and 13. The motor 4, located generally at 15, is centrallylocated in the housing 11. The motor 4 may be any conventional DCelectric motor used within fans, such as a single-phase or poly-phasemotor. The fan includes a winding circuit (discussed below withreference to FIGS. 4 and 6), a synchronization circuit (also discussedbelow with reference to FIGS. 4 and 6), and a stator, each of which aresupported in a fixed relation to the housing 11 in a central housingportion 16 that is connected to the venturi 14 by struts 17 of a spiderstructure. Leads 19 and 20 are brought out from the motor electronicsalong one strut 17. The strut 17 with the leads 19 and 20 is speciallyformed for this purpose with a longitudinal channel leading to a narrowgroove 23 at the outer periphery of the housing 11. The groove 23retains the leads 19 and 20 in the channel while directing them towardthe generally cylindrical exterior 25 of the housing 11 as shown.

[0023]FIG. 3 illustrates an impeller 30 of the fan 10 as shown in FIG.2. The impeller 30 includes fan blades 31 supported on a hub 32 (e.g.,manufactured from plastic), which in turn is secured to a rotor 35 ofthe fan motor 4. The rotor 35 has an annular permanent magnet 37 in asteel cup 38. A central shaft 39, which is secured to the end face ofthe cup 38, is received in bearings (not shown) in the stator assemblyof FIG. 2 when the fan 10 is assembled. Of course, the impeller 30 alsomay be a propellor or other similar apparatus utilized in fans.

[0024]FIG. 4 schematically shows an illustrative commutation circuit 46that rotates the rotor 35 at a reference frequency prescribed by themaster clock 6. In this embodiment, the commutation circuit 46 isentirely internal to a single motor 4. More particularly, FIG. 4schematically shows a commutation circuit 46 that has been configured toinclude a programmable device (e.g., a microprocessor) for synchronizingrotor speed with the reference signal generated by the master clock 6.Accordingly, the commutation circuit 46 may be considered to include aprogrammable device (referred to below as synchronization circuit 47)that synchronizes rotor speed with the reference signal.

[0025] The commutation circuit 46 includes a plurality of circuitelements that are coupled with a first coil (“coil A”), a second coil(“coil B”), and a center tap of the coils (identified by “CT”). As knownin the art, the coils interact with the magnet 37 of the rotor 35 toeffectuate rotor rotation. Accordingly, the circuit further includes afirst hall sensor 48 having a first output to a first switchingtransistor Q1, and a second output to a second transistor Q2. Eachtransistor Q1 and Q2 has a respective Zener diode D2 and D3 for limitingits respective collectors base voltage. The first hall sensor 48 ispowered by a power resistor R5 that is connected to its positiveterminal.

[0026] The commutation circuit 46 also includes a tachometer 50 formonitoring the rotation of the rotor 35. More particularly, thetachometer 50 includes a second hall sensor 52 positioned in a mannerthat enables it to sense the magnetic field produced by the magnet 37 ofthe impeller 30. In a manner similar to the first hall sensor 48, thesecond hall sensor 52 is powered by a resistor R2. In addition to itsprior noted elements, the commutation circuit 46 also includes anotherZener diode D1 with a series resistor R1 for voltage regulation, a ZenerD4 with resistor R6 to maintain constant input voltage, and a motorprotection device 58, such as a positive temperature coefficientthermistor (commonly referred to as a “PTC”). Use of the motorprotection device 58 helps to ensure that the fan motor windings areprotected from high current conditions.

[0027] In accord with illustrative embodiments of the invention, thecommutation circuit 46 also includes a synchronization circuit 47 (notedbriefly above) for synchronizing the rotation of the rotor 35 with thereference signal received from the master clock 6. To that end, thesynchronization circuit 47 includes a programmable device, such as aprocessor 54, that is programmed to synchronize the rotor speed with thereference signal. The processor 54 may be any processor known in theart, such as a model number MC68HC705 microprocessor, distributed byMotorola, Inc. of Schaumberg, Ill. The processor 54 operates at a ratespecified by an internal clock, such as an external oscillator 56. Notethat although referred to as “external,” the external oscillator 56 isinternal to and a part of the overall commutation circuit 46. It isreferred to as an external oscillator since it is external to theprocessor 54. In alternative embodiments, the processor 54 includes aninternal oscillator or other clocking device for timing its processes.

[0028] The exemplary processor 54 has twenty pins numbered from 1 to 20.The pins are coupled to the following elements:

[0029] pins 1 and 2: Both of these pins are connected to the externaloscillator 56 for receiving a timing signal to time its internalprocesses;

[0030] pin 3: This pin is an output to the first hall sensor 48 of thecommutation circuit 46 to control the energization of the first hallsensor 48 and, consequently, the rotational speed of the motor 4;

[0031] pins 4-6, 11-18: These pins are unused;

[0032] pin 7: This pin is a reference signal input that is coupled withthe master clock 6 to receive the external reference signal;

[0033] pin 8: This pin is a tachometer input that receives a speedsignal (identifying the speed of the rotor 35) from the tachometer 50;

[0034] pins 9 and 10: These pins receive power from a power supply (notshown);

[0035] pin 19: This pin is used to receive input data from a sensor,such as a temperature sensor; and

[0036] pin 20: This pin is coupled with a capacitor C2 and resistor R3,both of which are used for start-up delay and reset purposes.

[0037] A prototype built that should produce satisfactory results hasthe following element values:

[0038] R1: 100 ohms;

[0039] R2: 10,000 ohms;

[0040] R3: 2.4 megaohms;

[0041] R4: 1,000 ohms;

[0042] R5: 260 ohms;

[0043] C1: 0.01 microfarads; and

[0044] C2: 2.2 microfarads

[0045] D1 and D4: 5.1 volt Zener diodes; and

[0046] D2 and D3: 32 volt Zener diodes for a 12 volt applications.

[0047] It should be noted that all element values recited herein areexemplary and may be adjusted by those skilled in the art. Accordingly,these values are not intended to limit preferred embodiments of theinvention.

[0048] As known by those skilled in the art, if the first hall sensor 48is provided with a continuous source of power, it should switch thetransistors Q1 and Q2 at a rate that rotates the rotor 35 at the maximumrated speed of the motor 4. In illustrative embodiments, however, theprocessor 54 intermittently switches the power to the first hall sensor48 “off” and “on” in a carefully controlled manner to ensure that therotor 35 rotates at the rate prescribed by the master clock 6.Accordingly, the rotational speed of the rotor 35 typically should beless than the maximum rated speed of the motor 4.

[0049] In alternative embodiments of the invention, the reference signalmay derive from another source other than the master clock 6. Noexternal master clock 6 thus is necessary since one of the motors 4generates the reference signal. For example, the reference signal may bederived from the oscillator 56 in one of a plurality of coupled motors4. Accordingly, referring to FIGS. 1 and 4, the timing signal from theexternal oscillator 56 within motor 2 may be transmitted to motors 1, 3and 4. In such case, motors 1-4 thus may set their rotational speed tothe external oscillator 56 in motor 2.

[0050] In other embodiments, the tachometer 50 in one motor 4 generatesthe reference signal. Accordingly, the commutation circuit 46 shown inFIG. 4 also may include additional elements to effectuate this result.More particularly, the processor 54 may be preprogrammed to ascertain ifit is coupled with a sensor, such as a temperature sensor (not shown)that detects the temperature at a given location. If coupled with such asensor, then it is deemed the master motor 4 and thus, produces thereference signal. The master motor 4 therefore is in a master/slaverelationship with the other motors 4, where the other motors are slavemotors 4. Accordingly, the tachometer 50 also includes an output line52A to produce an output signal that is used as the reference signal forthe other slave motors 4. In this case, the tachometer output line 52Ais connected to pin 7 on the processors 54 in each slave motor 4.

[0051] By way of example, the processor 54 may be programmed to modifythe speed of the motors if the temperature sensed by the temperaturesensor is measured to be outside of a prespecified temperature range.When such a temperature is sensed, the processor 54 controls the motor 4to change its speed. This speed change consequently is detected by thetachometer 50, which responsively generates a new speed signal for themaster motor 4. The other slave motors 4 (i.e., their processors 54)consequently receive the changed reference signal (from the tachometer50 of the master motor 4), and adjust their speed appropriately.

[0052] In yet other embodiments, regardless of its source, the referencesignal may change during operation. For example, the master clock 6 mayhave a temperature sensor (discussed above) that detects the temperaturewithin a device being cooled. In a manner similar to the embodimentnoted above, if the temperature is outside of a preset temperaturerange, then the frequency of the reference signal may change in acorresponding manner to cause the motors to rotate at a different rate.

[0053] The master clock 6 may be manually adjustable so that it can bereprogrammed to change the frequency of the reference signal. To thatend, the master clock 6 may include a digital or analog display, knob,or other adjustment device that permits an operator to change thefrequency of the reference signal. Alternatively, the master clock 6 mayinclude programmable elements that permit the clock to be manuallyreprogrammed.

[0054] As noted above, the processor 54 is preprogrammed to execute inaccordance with a set of instructions. FIG. 5 shows one such processexecuted by the processor 54 for maintaining the rotor speed at apreselected rate. The process begins at step 500, in which the coils Aand B are energized to rotate the rotor 35 at its maximum speed. Forcingthe rotor 35 to its maximum speed reduces the effect of inertia ofstartup.

[0055] It then is determined at step 502 if the frequency of thereference signal received by the processor 54 is within a prescribedfrequency range. In illustrative embodiments, this frequency range ispreprogrammed into the processor 54. More particularly, the processormay be programmed to operate in a specified manner if the referencesignal is not within such prescribed frequency range. This permits themotor 4 first to determine that some error condition exists, and then tocompensate for the error condition appropriately. For example, themaster clock 6 may malfunction (e.g., crash), or the connection betweenthe master clock 6 and the processor 54 may become broken. In eithercase, the reference signal may not be received by the processor 54.Accordingly, the processor 54 detects this condition as having a zerofrequency, which is not within a prescribed frequency range that isgreater than zero. In response, the processor 54 executes variousprocesses to compensate for this condition. As another example, thereference signal may have a frequency that does not cause the motors torotate at a sufficiently rapid rate. For example, use of a referencesignal of this frequency could cause the motors 4 to not rotate rapidlyenough to cool electronic components within a computer housing. In thiscase, the processor 54 may detect that such frequency is too low, andcompensate appropriately.

[0056] In illustrative embodiments, the processor 54 compensates for areference signal being outside of the prescribed range by executingsteps 504 and 506. In particular, the processor continues to step 504,in which the rotational speed of the motor is set to a preselected speedpreprogrammed into the processor 54. This preselected speed isindependent of the reference signal. In illustrative embodiments, thispreselected speed is the maximum speed of the motor 4. In otherembodiments, the preselected speed is less than the maximum speed. Insuch case, the preselected speed is timed from the external oscillator56.

[0057] The process then continues to step 506, in which the processorsignals this error condition to some other module within the motor. Forexample, an error light (e.g., a light emitting diode, not shown) may beilluminated to visually indicate that an error condition exists. Whenused as one of a plurality of motors 4 (as shown in FIG. 1), anoticeable sound should occur at many speeds since the motors 4 now areno longer synchronously operating. In addition to the above noted errorlight, this noise may be considered an additional indicator of the errorcondition.

[0058] Returning to step 502, if the reference signal is determined tobe within the prescribed range, then the current speed (e.g., theswitching frequency of the transistors Q1 and Q2), as determined by thetachometer 50, is compared with the reference frequency in the referencesignal in accordance with conventional comparison processes (step 508).In exemplary embodiments, the reference signal may have a frequency of120 hertz. Accordingly, the frequency of the speed signal from thetachometer 50 (i.e., at this point in time, the maximum frequency), iscompared against 120 hertz.

[0059] It then is determined at step 510 if there is a differencebetween the reference signal and the speed signal. If such a differenceis determined, then the process continues to step 512, in which theprocessor 54 adjusts current speed of the rotor 35 appropriately. Forexample, the speed may be reduced a preselected amount from the maximumspeed. As noted above, the processor 54 reduces the speed by switchingthe power to the first hall sensor 48 “off” and “on” in a controlledmanner.

[0060] If, however, at step 510 it is determined that there is nodifference between the reference signal and the speed signal, then theprocess skips to step 514, in which the processor 54 waits for the nexthalf rotation of the rotor 35, and then loops back to step 502 todetermine if the reference signal is within the prescribed frequencyrange. Accordingly, the speed of the rotor 35 preferably is checked and,if necessary, adjusted about every half revolution of the rotor 35. Thisprocess continues until the motor 4 no longer is operating. Of course,in illustrative embodiments, the reference signal is the same as thatreceived by each of the parallel motors 4 (i.e., fans) in the motorapparatus 2 shown in FIG. 1. This consequently causes each motor 4 tooperate at approximately the same speed.

[0061] As noted above, the processor 54 is preprogrammed to execute theprocess shown in FIG. 5 to effectuate synchronous rotation of each motor4. In preferred embodiments, assembly language specific to the processor54 is used. In other embodiments, any language that can be processed bythe processor 54 may be used.

[0062] The frequency of the reference signal may be used to control therotational speed, via the process shown in FIG. 5, in various differentways. In the embodiment discussed with regard to FIG. 5, for example,the processor 54 is programmed to rotate the rotor 35 at a speed thatcorresponds directly to the frequency of the reference signal. Forexample, if the reference signal has a frequency of 120 hertz, then theprocessor 54 rotates the rotor 35 at a rate of 120 hertz. In otherembodiments, the processor 54 is programmed to rotate the rotor 35 atsome whole or fractional multiple of the frequency of the referencesignal. In yet other embodiments, the frequency of the reference signalmay be used as input into a mathematical function that determines aspecific speed for rotating the rotor 35. Accordingly, the frequency ofthe reference signal may be considered to be a baseline frequency thatis used in some manner to calculate a rotational frequency for a motor4.

[0063]FIG. 6 shows an alternative embodiment of the invention, in whichthe commutation circuit includes four transistors Q3-Q6 configured as anH-bridge (referred to herein as “H-bridge”). In particular, the H-bridgeuses transistors Q3-Q6 to permit substantially 100% of the coils to beused in either direction without requiring a center-tap. To that end,the processor (identified in this figure as microprocessor U7) isprogrammed to switch transistors Q4 and Q6 “on” and “off” at a selectedfrequency via respective pins 8 and 11. No more than one of transistorsQ4 and Q6 is turned on at any given time.

[0064] Energization of transistor Q6 consequently energizes transistorQ3. When in such state, current flows through coil inputs T1 and T2 inone direction. In a similar manner, energization of transistor Q4consequently energizes transistor Q5. When in this state, the currentflows in the opposite direction through the coil inputs T1 and T2. In amanner similar to the circuit shown in FIG. 4, the microprocessor U7switches the transistors “on” and “off” at a rate as prescribed by thereference signal to facilitate rotation of the rotor 35 at a specifiedrate.

[0065] As previously noted, the processor 54 in FIG. 4 cooperates withthe first hall sensor 48 to control switching of its respectivetransistors Q3 and Q4. Unlike the circuit shown in FIG. 4, however, themicroprocessor U7 in FIG. 6 directly controls the switching of thetransistors without requiring that a hall sensor be connected to thetransistors Q3-Q6. The microprocessor does use a hall sensor HS1,however, to receive a speed signal representing the rotational speed ofthe rotor 35. To that end, pins 1 and 4 of microprocessor U7 areconnected to hall sensor HS1, which acts as a tachometer. Accordingly,as discussed with reference to FIG. 5, the microprocessor U7 controlsthe rotation of the rotor 35 by comparing the reference frequency withthe speed signal received from HS1.

[0066] In some embodiments, the microprocessor may serve to synchronizethe rotor 35 with the reference signal only. In other embodiments,however, the microprocessor U7 can direct further tasks. For example,the commutation circuit shown in FIG. 6 includes a pair of optocouplersU1 that forward tachometer and fan performance data received from themicroprocessor U7.

[0067] It is expected that preferred embodiments can control a widerange of rotational speeds. For example, preferred embodiments shouldcontrol motors 4 that are rated to rotate at commonly used speed ratiosranging from 600 to 6,000 revolutions per minute, while synchronizingfan speeds (of multiple fans) to within 1.5 revolutions per second. Ofcourse, many embodiments should control motors 4 operating at speedsoutside of this range. Moreover, preferred embodiments should bescalable to control a large number of motors 4 that are controlled inthe manner described herein. Since there is a minimum of components(i.e., by using the processor 54 or U7), the synchronization circuit 47can be integrated with existing motor commutation circuits.

[0068] As suggested above, the disclosed apparatus and method may beimplemented as a computer program product for use with a computersystem. Such implementation may include a series of computerinstructions fixed either on a tangible medium, such as a computerreadable medium (e.g., a diskette, CD-ROM, ROM, or fixed disk) ortransmittable to a computer system, via a modem or other interfacedevice, such as a communications adaptor connected to a network over amedium. The medium may be either a tangible (e.g., optical or analogcommunications lines) or a medium implemented with wireless techniques(e.g., microwave, infrared, or other transmission techniques).

[0069] The series of computer instructions embodies all or part of thefunctionality previously described herein with respect to the system andmethod. Those skilled in the art should appreciate that such computerinstructions can be written in a number of programming languages for usewith may computer architectures or operating systems. Further, suchinstructions may be stored in any memory device, such as asemiconductor, magnetic, optical or other memory devices, and may betransmitted using any communications technology, such as optical,infrared, microwave, or other transmission technologies. It is expectedthat such a computer program product may be distributed as a removablemedium with accompanying printed or electronic documentation (e.g.,shrink wrapped software), pre-loaded with a computer system (e.g., onsystem ROM or fixed disk), or distributed from a server or electronicbulletin board over a network (e.g., the Internet or World Wide Web). Ofcourse, some embodiments of the invention may be implemented as acombination of both software (e.g., a computer program product) andhardware. Still other embodiments of the invention are implemented asentirely hardware, or entirely software (e.g., a computer programproduct).

[0070] Although various exemplary embodiments of the invention have beendisclosed, it should be apparent to those skilled in the art thatvarious changes and modifications can be made which will achieve some ofthe advantages of the invention without departing from the true scope ofthe invention. These and other obvious modifications are intended to becovered by the appended claims.

We claim:
 1. A DC electric motor comprising: a rotor capable of rotatingat a rotational speed; rotor circuitry that controls the rotationalspeed of the rotor; an input to receive an external reference signalindicating a preset speed; a programmable element operatively coupledwith the input and the rotor circuitry within the motor, theprogrammable element being capable of comparing the external referencesignal with the rotational speed of the rotor, the programmable elementcontrolling the rotor circuitry based upon the comparison of theexternal reference signal and the rotational speed of the rotor.
 2. TheDC electric motor as defined by claim 1 wherein the programmable elementis a processor.
 3. The DC electric motor as defined by claim 1 whereinthe programmable element is capable of controlling the rotor circuitryto increase the rotational speed of the rotor if it is determined thatthe rotational speed of the rotor is less than the preset speedindicated in the external reference signal.
 4. The DC electric motor asdefined by claim 1 wherein the programmable element is capable ofcontrolling the rotor circuitry to decrease the rotational speed of therotor if it is determined that the rotational speed of the rotor isgreater than the preset speed indicated in the external referencesignal.
 5. The DC electric motor as defined by claim 1 wherein the rotorcircuitry includes commutation circuitry.
 6. The DC electric motor asdefined by claim 1 further including: a housing containing the rotorcircuitry and programmable element.
 7. The DC electric motor as definedby claim 1 wherein the programmable element is programmed to detect anerror condition with the external reference signal, the programmableelement setting the rotational speed of the rotor to a selected speed ifthe error condition is detected.
 8. The DC electric motor as defined byclaim 7 wherein the error condition is considered to have occurred ifthe preset speed is not within a prescribed range of speeds.
 9. The DCelectric motor as defined by claim 7 further comprising: an internalclock producing an internal clock signal, the selected speed being basedupon the internal clock signal.
 10. The DC electric motor as defined byclaim 1 further comprising: an impeller coupled with the rotor.
 11. Amotor apparatus comprising: a first DC electric motor capable ofrotating at a first rotational speed and having a first internalprocessor; and a second DC electric motor capable of rotating at asecond rotational speed and having a second internal processor; and amaster clock that produces a reference signal indicating a preset speed,the master clock being coupled with both the first DC electric motor andthe second DC electric motor, the first processor being capable ofcontrolling the first rotational speed to be synchronized with thereference signal, the second processor being capable of controlling thesecond rotational speed to be synchronized with the reference signal.12. The motor apparatus as defined by claim 11 wherein the first DCelectric motor includes a first impeller, and the second DC electricmotor includes a second impeller.
 13. The motor apparatus as defined byclaim 11 wherein the first processor includes a first reference input,and the second processor includes a second reference input, the firstand second reference inputs being coupled with the master clock toreceive the reference signal.
 14. The motor apparatus as defined byclaim 11 wherein the first rotational speed and second rotational speedare substantially identical.
 15. The motor apparatus as defined by claim11 further comprising: a first motor housing containing the first DCelectric motor; and a second motor housing containing the second DCelectric motor.
 16. The motor apparatus as defined by claim 11 whereinthe first DC electric motor includes commutation circuitry that iscontrolled by the first processor.
 17. The motor apparatus as defined byclaim 11 wherein the first internal processor is programmed to detect anerror condition with the reference signal, the first internal processorsetting the first rotational speed to a selected speed if the errorcondition is detected.
 18. The DC electric motor as defined by claim 16wherein the error condition is considered to have occurred if the presetspeed is not within a prescribed range of speeds.
 19. The DC electricmotor as defined by claim 16 wherein the first internal processorincludes an internal clock that produces an internal clock signal, theselected speed being based upon the internal clock signal.
 20. A DCelectric motor comprising: a rotor capable of rotating at a rotationalspeed; rotor circuitry that controls the rotational speed of the rotor;means for receiving an external reference signal indicating a presetspeed; means for comparing the external reference signal with therotational speed of the rotor, the comparing means including means forcontrolling the rotor circuitry based upon the comparison of theexternal reference signal and the rotational speed of the rotor, thecomparing means being internal to the motor.
 21. The DC electric motoras defined by claim 20 wherein the comparing means is a processor. 22.The DC electric motor as defined by claim 20 wherein the comparing meansincludes means for controlling the rotor circuitry to increase therotational speed of the rotor if it is determined that the rotationalspeed of the rotor is less than the preset speed indicated in theexternal reference signal.
 23. The DC electric motor as defined by claim20 wherein the comparing means includes means for controlling the rotorcircuitry to decrease the rotational speed of the rotor if it isdetermined that the rotational speed of the rotor is greater than thepreset speed indicated in the external reference signal.
 24. The DCelectric motor as defined by claim 20 wherein the rotor circuitryincludes commutation circuitry.
 25. The DC electric motor as defined byclaim 20 further including: a housing containing the rotor circuitry andcomparing means.
 26. The DC electric motor as defined by claim 20wherein the comparing means includes means for detecting, an errorcondition with the external reference signal, the comparing meanssetting the rotational speed of the rotor to a selected speed if theerror condition is detected.
 27. The DC electric motor as defined byclaim 26 wherein the error condition is considered to have occurred ifthe preset speed is not within a prescribed range of speeds.
 28. The DCelectric motor as defined by claim 26 further comprising: an internalclock producing an internal clock signal, the selected speed being basedupon the internal clock signal.
 29. The DC electric motor as defined byclaim 20 further comprising: an impeller coupled with the rotor.
 30. Arotor circuit for controlling the speed of a rotor, the rotor being apart of a DC electric motor, the rotor circuit comprising: switchingcircuitry that, at least in part, controls the rotational speed of therotor; an input for receiving an external reference signal indicating apreset speed; and a programmable element operatively coupled with theinput and the switching circuitry, the programmable element comparingthe speed of the rotor with the preset speed indicated in the referencesignal, the programmable element controlling the switching circuitrybased on the comparison of the preset speed and the speed of the rotor,the switching circuitry and programmable element being internal to themotor.
 31. The rotor circuit as defined by claim 30 wherein the motorincludes a stator with coils, the switching circuitry transmittingcurrent to the coils based upon the rotational position of the rotor.32. The rotor circuit as defined by claim 30 wherein the programmableelement is a processor.
 33. The rotor circuit as defined by claim 30wherein the programmable element is capable of controlling the switchingcircuitry to increase the speed of the rotor if it is determined thatthe speed of the rotor is less than the preset speed indicated in theexternal reference signal.
 34. The rotor circuit as defined by claim 30wherein the programmable element is capable of controlling the switchingcircuitry to decrease the speed of the rotor if it is determined thatthe speed of the rotor is greater than the preset speed indicated in theexternal reference signal.
 35. The rotor circuit as defined by claim 30wherein the programmable element is programmed to detect an errorcondition with the external reference signal, the programmable elementsetting the speed of the rotor to a selected speed if the errorcondition is detected.
 36. The rotor circuit as defined by claim 35wherein the error condition is considered to have occurred if the presetspeed is not within a prescribed range of speeds.
 37. The rotor circuitas defined by claim 35 further comprising: an internal clock producingan internal clock signal, the selected speed being based upon theinternal clock signal.